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GAS DETECTION

Published: 10th Mar 2011

Rob Fair, Chair of the Institution of Occupational Safety and Health’s Hazardous Industries Group, discusses gas detection with his committee members.

Natural gas is a widely used commodity around the world, especially in the Middle East, which has plentiful and hugely profitable sources of the fossil fuel. In industry, gas is sourced, used and produced in numerous forms, and always carries with it acute dangers. But where these are not respected and planned for, it can cause harm to people and the environment - and that’s what makes gas detection so crucial.

Members of the Institution of Occupational Safety and Health’s (IOSH) Hazardous Industries Group encourage best practice methods for leak prevention, detection and dispersion, and protection of employees, the public, and the environment. As gases are so commonly used, these examples of best practice are equally relevant to the Middle East, as they are to the UK, Europe, North America and around the globe.

Industries that use gas detection

The most common gases produced in the hazardous industries are carbon monoxide, chlorine, hydrogen fluoride, hydrogen sulphide, ammonia and flammable substances. Typically these gases are found in the production of iron and steel, chemicals and petrochemicals, oil refining, natural gas sourcing, refrigeration and water treatment.

Some gases - namely toxic and flammable - need more urgent and early detection. However, the need for speed of detection of any gas will depend on its type, temperature, pressure, quantity, toxicity, proximity to employees and public, effectiveness of counteractive measures, and any medical intervention available.

Petrochemical plants carry a high risk of gas leakage, which can lead to explosion or fire that not only damages equipment, but puts lives at serious risk.

Nuclear power stations also use gases such as CO2, as coolant, to transfer heat to generate steam and to prevent reactor overheating. Any loss of CO2 could reduce the efficiency of heat removal and cause overheating. In both of these situations gas detectors are used not only to keep the process going, but keep people safe.

The coke produced in making iron and steels gives off carbon monoxide. Process fluids or solvents produced in the chemical and petrochemical industries can be extremely flammable themselves, as can the actual chemicals actually used in the processes like chlorine or benzene.

Oil refining hazards include hydrogen sulphide, hydrofluoric acid and other flammability issues, while the oil and gas drilling industry is also extremely hazardous. Disasters in recent years expose the need for prior warning systems that pick up even the most minute escape of gas.

David Hughes, health and safety consultant and a core member of IOSH’s Hazardous Industries Group, said: “Even nitrogen, which might not be seen as one of the most hazardous of gases, is also an asphyxiant and needs to be handled with respect. We also consider carbon dioxide fire extinguishers in confined spaces, as they reduce the oxygen in an atmosphere, making it difficult to breathe.”

How gas escapes

Any system which uses, generates, or contains a gas under pressure can develop leaks. The causes of a leak will depend on the type of gas being used, the process it is being used in, and any products or reactions generated in that process, and the quantity that could be released.

Knowing the points and times gas is likely to escape will help to determine where detectors should be placed, and how sensitive they need to be. There are many factors that cause leaks, but typically, human fallibility, corrosion, fatigue, accelerated chemical reactions causing increased pressure, poor maintenance and faulty equipment can all play a part.

Fatigue of equipment is a big problem, and wear and tear is often related to poor and inadequate maintenance. Failed pipe work, poor piping joints, leaking pumps or valve seals, or vents and drains can become the culprits if they are not kept in good condition.

David Hughes said: “Any instrument needs regular testing and calibration, and that will make sure equipment and processes comply with standards. Lack of adequate maintenance is so often the cause of gas leaks and the sad thing is that this is one of the most avoidable causes.”

Erosion from weather and corrosion from substances have an effect on a system’s ability to contain gas, while breaks in sealing or piping can also provide a leak path.

However, some types of gas can also cause issues in confined spaces, and workers can find themselves in a situation where the atmosphere can’t support breathing, so detection will be a part of the risk reduction measures. Similarly, working around stagnant water that gives off sulphur, or other gases from decaying bacteria will also require risk assessment.

Joshua Rice, Hazardous Industries Group vice chair, said: “There are a lot of unexpected situations where people can put themselves in harm’s way if they aren’t aware of the gases produced where they are working, or by what they’re doing.

“Even setting concrete gives off carbon dioxide - which can act as an asphyxiant in the right conditions. Organic food or waste can remove oxygen, producing hydrogen and methane as it decomposes. So anyone working in an enclosed environment needs to be aware of the oxygen left in that atmosphere, and that’s something detection can help with,” he added.

Gas detection methods

Most systems can be broken down into two categories - fixed and portable. The early detection systems for gas were very basic, but the principles remain the same to this day.

For instance, the use of canaries in coal mines was later replaced by Davy Safety Lamps, and these can still be used by an individual wherever they are working.

Nowadays, modern electronic personal gas detection monitors allow an individual to work in a potentially hazardous area, by sounding an alarm when the gas rises to an unacceptable level. Safe working levels are well documented in literature, but these do vary from country to country.

Portable detection is used to help workers undertaking tasks such as maintenance, where employees might disturb release gas that wouldn’t normally roam free in that environment. Portable devices can also be used for sampling, where workers need to measure the quality of the atmosphere before entering an area.

Fixed systems are used in the main to protect many employees at a time. Where they are placed in a building will depend on whether the gas is heavier or lighter than air. Everyone is familiar with smoke alarms and carbon monoxide detectors - perhaps the two most common methods of fixed gas detection.

Another advantage of fixed gas detection is that the gas detector will monitor an area constantly, so that if an operator is not present full time, the gas leak will still be detected and the appropriate emergency response can be undertaken.

Gas detection outside requires many detectors to provide blanket coverage across a wide area around a plant or a release point. This is because without the restriction of building walls and structures, the gas can escape in any direction depending on wind and weather conditions at the time. In these circumstances, gas detectors can cover a number of typically predictable sources of leak, such as corrosion points, sampling points which might get left open by human error, and road, rail or marine loading and unloading locations.

The sensitivity of the gas detection device must reflect a substance’s lower explosive limit or toxic levels, to give early warning of any danger.

Glenn Sibbick, Hazardous Industries Group committee member and projects director for Centrica Storage Ltd, uses various techniques depending on the gas.

Having also presented at the fourth Annual Safety Conference in Doha two years ago, he said: “Monitoring general hydrocarbon gases such as methane, ethane, or propane during oil and gas exploration or production, protects the local area against fire or explosion. Here, detectors are placed at potential leak sources. The detector is set to detect a gas depending on which one is the most dominant, as in most gas fields there will be a mixture of such gases, with each gas varying in concentration.”

How companies prepare for potential gas leaks

From the perspective of Joshua Rice, occupational hygiene manager for Sellafield Ltd, fundamentally, to ensure safety when using harmful gases, companies need to understand three main areas:

• Process control, to ensure that the presence, pressure, reactions, and concentration of any harmful gases are controlled so that the gases do not escape into the environment

• Loss prevention, will ensure good design, maintenance, inspection, and corrosion prevention are in place to ensure that gases are contained

• Loss preparedness, with good gas detection and process monitoring to identify the loss of gas if it occurs and suitable emergency arrangements to protect those who may be harmed

The latter of these is obviously a key focus for IOSH. Because of the organisation’s core aim of protecting people while at work, this means gas detection is essential for workers’ health and safety.

Joshua Rice said: “Any hazardous industry will take a structured review of any risks to a plant, people, and the environment - and that will include gas detection. The key is to ensure?defence in depth, with a number of different elements of protection proportionate to the level of risk.

“For example, a small cylinder of CO2 does not need as much inspection and risk control when compared to one that contains 20m3 - this is common sense.”

Part of the health and safety process for selecting gas detection often involves gas dispersion modelling, using likely locations where the substance could escape, modelling a varying of densities, volumes, temperatures of the gas, along with differing weather conditions to find out how the gas cloud is likely to form and disperse in the event of a leak. ‘Hazops’ - hazard and operability studies - carry out examination of equipment and operation of the equipment to determine potential points where gas maybe released.

Glen Sibbick said: “Companies often face the risk of gas contamination, whether they operate within a plant or otherwise. By installing automatic process control systems, they can make sure they keep control of the plant in the event of a leak, usually through emergency shutdown and a depressurisation system that would prevent a domino effect, causing the situation to spiral out of control.”

Employee training

Basic training for workers in the hazardous industries takes two forms - an operational response in the event of an alarm, and an emergency response to limit the spread, or the effect of gas that has already escaped.

Various training programmes exist for the design, installation and operation of detectors. Employees also get general training on how to work in a hazardous environment, and what to do if there is a leak to avoid asphyxiation, injuries from explosion of fire, or skin damage due to toxicity.

Anyone working in confined spaces will also receive training in detection and assessment of the gas types present. Testers working in these conditions will obviously be trained in the specific detection equipment they’re using.

Glen Sibbick added: “It’s quite normal to have watch men, whose only responsibility is to monitor the activity around the detectors. They don’t get involved in the work tasks to free them up to spot the early warning signs of gas ingress or generation. These people will also manage any escape support equipment required to ensure safe egress in the event of the gas detector going into alarm.”

Of the personal protective equipment (PPE) generally worn, and the additional items worn in the event of a leak, Joshua Rice said: “There is a wide range of PPE that workers are trained to wear both in their day-to-day jobs, and in the case of an emergency when there’s been a gas leak. We use CO2 personal detection meters, and self contained breathing apparatus in areas where the percentage of oxygen is less than 19 percent.

“In the case of flammable gas leaks, anti-flash suits and intrinsically safe equipment is often required.”

Part of the training process to prevent and deal with potential disaster involves regular emergency response practice - this includes testing alarms and carrying out dummy evacuations. In an emergency, there will be a safe haven to stay in until the all-clear is sounded and anyone responding to the incident will approach up-wind, wearing appropriate PPE for the hazard.

Who is responsible for gas detection policy?

Health and safety decisions within the hazardous industries are likely to be ratified at board level. The board will view safety reports that have been compiled by multidisciplinary experts, who will detail potential major hazard events that could occur within the organisation. This provides a framework for the company to put equipment and procedures in place to reduce the risks.

Most hazardous industries will utilise ‘Hazan’ (Hazard Analysis) and ‘Hazop’ (Hazard and Operability) studies to identify risks with process plant and operations. The results from these studies tell a business what level and standards of gas detection are required to keep their plant, people and the environment safe.

David Hughes said: “While the UK and European requirements are different to the Middle East, it’s fair to say that over the years the acceptable exposure limits have been reducing, either for safety or environmental reasons.”

As exposure limits are reduced, Hazans and Hazops will need reviewing to ensure that gas releases and losses are reduced in line with the new exposure levels. In some cases this may require additional engineering to reduce the likelihood or significance of any gas releases.

Detection failures to learn from

There have been numerous fatalities where leaked CO2 has caused asphyxiation to workers, while flammable gas leaks have led to explosions and fires, causing loss of life.

The most recent tragedy is the Deepwater Horizon, where a blowout from a natural gas leak in the Gulf of Mexico in May 2010 caused a fatal explosion and fire, killing 11 people. In 2005, 15 were killed and around 170 injured at Texas City when a cold vent system allowed oil production hydrocarbons to be released into the atmosphere, which ignited.

In 1988 the UK Piper Alpha Disaster claimed the lives of 127 people when a leak of natural gas ignited, causing damage to fire protection and secondary fires on the offshore platform. That remains the worst offshore and gas incident in history. The resulting legislation proposed by Lord Cullen in his post-tragedy enquiry reshaped the offshore industry, and all of his findings have now been implemented, or at the very least considered across the whole of the offshore oil and gas industry.

Lessons from IOSH’s Hazardous Industries Group

The IOSH Hazardous Industries Group Peer Review Process is soon to be launched. This will provide a template to help companies across related industries and wider explore each other’s health and safety systems, events, and experiences.

The group believes that across the different sectors, the knowledge of how to manage and further control risks already exists. By sharing best practice and sourcing and implementing improvements, ideas can infiltrate companies not only throughout the UK and Europe, but in the Middle East, where oil and gas drilling is a prominent, but hazardous industry.

Through this project, the group will be able to publish good practice and hazard identification examples so that they can be used by a range of companies.

Part of this will be to ensure that gas hazards become better identified, reduced and managed, and that contingencies are put in place to deal with any loss or emergency that may occur.

Author

IOSH is the Chartered body for health and safety professionals. With more than 38,000 members in 85 countries, it is the world’s biggest professional health and safety organisation.

IOSH sets standards, and supports, develops and connects its members with resources, guidance, events and training. The organisation is the voice of the profession, and campaigns on issues that affect millions of working people.

IOSH was founded in 1945 and is a registered charity with international NGO status. www.osedirectory.com/health-and-safety.php

Published: 10th Mar 2011 in Health and Safety Middle East

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Rob Fair